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    <meta charset="UTF-8">
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    <title>Document</title>
</head>
<body>
    <select>
        <option value="-1">城市</option>
        <option value="1">北京</option>
        <option value="2">上海</option>
        <option value="3">深圳</option>
        <option value="4">广州</option>
    </select>
    <script>
        let oMenu = document.getElementsByTagName('select')[0];
        oMenu.onchange = function(){
            console.log(oMenu.value);
        }
    </script>
</body>
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